Generally, a vehicle is equipped with a battery for storing electric energy to be supplied to various electric parts. For instance, an electric vehicle running only by an electric motor is equipped with a large capacity of battery to repeatedly run by charging the battery with an external charger. For charging this type of a vehicle battery, not only an electric vehicle but also, for example, a hybrid vehicle running by a combination of an electric motor and an internal combustion engine, the electric energy is recovered as a regenerative energy to be stored on the battery while running. In addition to it, the battery is sometimes made chargeable from an external charger. Further, since various types of fuel are converted into the electric energy in a fuel cell powered vehicle, the battery for storing the converted electric energy can be charged from an external charger.
This type of vehicle battery is subject to the influence of external environments such as an external temperature, in some cases. An example is that when the battery has a low temperature when it is charged, the charging efficiency will degrade. Therefore, there is a proposal for using an air conditioner of the vehicle to flow hot wind to the battery side so that the battery can be warmed to fall within a temperature range in which the battery can be charged in an efficient manner (examples are Patent Documents 1 to 3).
In these years, the quick charge of the vehicle battery is enabled for widespread use. In particular, since the charging efficiency degrades under the low-temperature condition below the freezing point, the quick charge would be made impossible. Hence, it is important to warm the battery to fall within the most suitable temperature range quickly.